Water filling and electric field-induced enhancement in the mechanical property of carbon nanotubes.

Ye HF, Zheng YG, Zhang ZQ, Chen Z, Zhang HW - Sci Rep (2015)

Bottom Line:
The effects of water filling and electric field on the mechanical property of carbon nanotubes (CNTs) are investigated with molecular dynamics simulations.The simulation results indicate that the water filling and electric field could enhance the elastic modulus but reduce the Poisson's ratio of the CNTs.The present findings provide a valuable route for the optimized design and application of the nanoscale functional devices based on the water-filled CNTs.

ABSTRACTThe effects of water filling and electric field on the mechanical property of carbon nanotubes (CNTs) are investigated with molecular dynamics simulations. The simulation results indicate that the water filling and electric field could enhance the elastic modulus but reduce the Poisson's ratio of the CNTs. As for the buckling behaviors, a significant enhancement could be observed in the yield stress and average post-buckling stress of the CNTs. In particular, the enhancement in the yield stress induced by the water filling and electric field could be even higher than that resulted from the solid filling. Moreover, a transition mechanism from the rod instability to shell buckling is shown to explain the nonmonotonic variation of yield stress, and the critical diameter can be tuned through filling the water molecules and applying the electric field. The present findings provide a valuable route for the optimized design and application of the nanoscale functional devices based on the water-filled CNTs.

f1: The stress-strain relationships.(a) the empty CNTs, (b) the water-filled CNTs and (c) the water-filled CNTs under the axial electric field with the intensity of 0.5 V/Å. The insets are the final buckling modes of the (8, 8) and (16, 16) CNTs. The color in the CNTs represents the distribution of the strain energy (eV) under the strain of about 23%.

Mentions:
Figure 1 shows the variations of the stresses with the strains of the empty CNTs, the water-filled CNTs and the water-filled CNTs under the electric field of 0.5 V/Å, respectively. In this work, the stress σ is calculated by the classical definition: σ = F/A, in which F is the spring force and A is the initial sectional area of CNTs. In the calculation of the sectional area, the thickness of CNTs is adopted as 0.66 Å22. From the figure, it can be seen that the stress linearly increases as the compressive strain increases in the initial elastic stage. Subsequently, when the strain reaches the critical buckling strain, the stress sharply decreases and the CNTs begin to buckle. For the buckled CNTs, the stress slowly decreases with the increase in the strain, and the variation range of the stress in this stage is rather small even though the strain keeps growing up to ~26%. The final buckling modes and the distributions of strain energy of the (8, 8) and (16, 16) CNTs are inserted in Fig. 1. The computational results reveal that the CNTs always present the asymmetric buckling mode in the final stage, which is similar to the common rod buckling. As compared to the (8, 8) CNTs, based on the global buckling deformation, some local wrinkles appear on the wall of the empty (16, 16) CNTs. For the water-filled CNTs, the CNTs look plump due to the filling of water molecules, and the local wrinkles on the wall of (16, 16) CNTs reduces. When the axial electric field is applied, the local wrinkles on the wall of (16, 16) CNTs almost disappear. Moreover, we can find that the high strain energy is always located on the positions of the large bending deformations along the CNTs. The average strain energies per carbon atom of the empty (8, 8) and (16, 16) CNTs under the strain of ~23% are 0.10 and 0.08 eV, respectively. After filling with water molecules, the corresponding average strain energies increase to 0.12 and 0.11 eV. Considering the electric field with the intensity of 0.5 eV/Å, a slight increase can still be observed for the average strain energies of the two CNTs. It is implied that under the same compressive strain, the water filling and electric field may speed up the compressive failure of CNTs, which is significant for the drug release and provides a reference point for the CNTs serving as a nanoscale fluid container.

f1: The stress-strain relationships.(a) the empty CNTs, (b) the water-filled CNTs and (c) the water-filled CNTs under the axial electric field with the intensity of 0.5 V/Å. The insets are the final buckling modes of the (8, 8) and (16, 16) CNTs. The color in the CNTs represents the distribution of the strain energy (eV) under the strain of about 23%.

Mentions:
Figure 1 shows the variations of the stresses with the strains of the empty CNTs, the water-filled CNTs and the water-filled CNTs under the electric field of 0.5 V/Å, respectively. In this work, the stress σ is calculated by the classical definition: σ = F/A, in which F is the spring force and A is the initial sectional area of CNTs. In the calculation of the sectional area, the thickness of CNTs is adopted as 0.66 Å22. From the figure, it can be seen that the stress linearly increases as the compressive strain increases in the initial elastic stage. Subsequently, when the strain reaches the critical buckling strain, the stress sharply decreases and the CNTs begin to buckle. For the buckled CNTs, the stress slowly decreases with the increase in the strain, and the variation range of the stress in this stage is rather small even though the strain keeps growing up to ~26%. The final buckling modes and the distributions of strain energy of the (8, 8) and (16, 16) CNTs are inserted in Fig. 1. The computational results reveal that the CNTs always present the asymmetric buckling mode in the final stage, which is similar to the common rod buckling. As compared to the (8, 8) CNTs, based on the global buckling deformation, some local wrinkles appear on the wall of the empty (16, 16) CNTs. For the water-filled CNTs, the CNTs look plump due to the filling of water molecules, and the local wrinkles on the wall of (16, 16) CNTs reduces. When the axial electric field is applied, the local wrinkles on the wall of (16, 16) CNTs almost disappear. Moreover, we can find that the high strain energy is always located on the positions of the large bending deformations along the CNTs. The average strain energies per carbon atom of the empty (8, 8) and (16, 16) CNTs under the strain of ~23% are 0.10 and 0.08 eV, respectively. After filling with water molecules, the corresponding average strain energies increase to 0.12 and 0.11 eV. Considering the electric field with the intensity of 0.5 eV/Å, a slight increase can still be observed for the average strain energies of the two CNTs. It is implied that under the same compressive strain, the water filling and electric field may speed up the compressive failure of CNTs, which is significant for the drug release and provides a reference point for the CNTs serving as a nanoscale fluid container.

Bottom Line:
The effects of water filling and electric field on the mechanical property of carbon nanotubes (CNTs) are investigated with molecular dynamics simulations.The simulation results indicate that the water filling and electric field could enhance the elastic modulus but reduce the Poisson's ratio of the CNTs.The present findings provide a valuable route for the optimized design and application of the nanoscale functional devices based on the water-filled CNTs.

ABSTRACTThe effects of water filling and electric field on the mechanical property of carbon nanotubes (CNTs) are investigated with molecular dynamics simulations. The simulation results indicate that the water filling and electric field could enhance the elastic modulus but reduce the Poisson's ratio of the CNTs. As for the buckling behaviors, a significant enhancement could be observed in the yield stress and average post-buckling stress of the CNTs. In particular, the enhancement in the yield stress induced by the water filling and electric field could be even higher than that resulted from the solid filling. Moreover, a transition mechanism from the rod instability to shell buckling is shown to explain the nonmonotonic variation of yield stress, and the critical diameter can be tuned through filling the water molecules and applying the electric field. The present findings provide a valuable route for the optimized design and application of the nanoscale functional devices based on the water-filled CNTs.